With the improvement on science and technology, a detection-type lighting device has been common in people's lives. In general, most of detection-type lighting devices are equipped with passive infrared (PIR) sensors, which detect whether there is any heat source, e.g. human body, entering a monitored zone. The sensing principle of a PIR is to detect the environmental temperature variation in the monitored zone, and generate a voltage value when variation occurs. Then it is determined whether the voltage value lies within a voltage range supposed to be generated in response to the motion of the heat source. If positive, the detection-type lighting device conducts light emission.
It is known the environmental temperature would significantly affect the sensing result of a PIR sensor. However, the environmental temperature around a detection-type lighting device inevitably varies with time. For example, the temperature in the daytime is typically higher than that in the nighttime; and the temperature in summer in northern hemisphere is generally higher than that in spring. Due to the temperature drift phenomena of the environmental temperature as exemplified above, the sensing result of the PIR sensor might fail to appropriate reflect the condition that a heat source is entering the monitored zone.
In an example, a threshold value for generating voltage sensing signals when the PIR sensor detects a human body is set to be 1.2V when the detection-type lighting device leaves factory. Therefore, the voltage sensing signals reaching 1.2V will result in light emission of the detection-type lighting device. On the other hand, any voltage sensing signal lower than 1.2V will be considered as noise, so no light emission will be conducted by the detection-type lighting device. However, the threshold value 1.2V set when leaving factory is a common voltage value set at a specified temperature, for example in winter. When the environmental temperature rises with season change to, for example, summer, the voltage value might rise up to 1.3V due to the higher environmental temperature. Accordingly, the voltage sensing signals generated when the PIR detects a human body, if detected to be 1.2V at this environmental temperature, will be determined as noise, so light emission should not be conducted by the detection-type lighting device. Since the threshold value is constant, erroneous action probably occurs for light emission, and the effect of intelligent illumination cannot be well performed.
For ameliorating the drawbacks, U.S. Pat. No. 6,288,395 discloses a sensor system includes combined PIR and temperature transducer, which uses the temperature transducer to detect environmental temperature. According to the sensing result of the temperature transducer, sensitivity of the PIR is tuned correspondingly so as to actually reflect the condition that a heat source is entering the monitored zone. However, according to U.S. Pat. No. 6,288,395, a temperature transducer is additional required, so the burden in cost and complexity in assembling are raised due to the additional temperature transducer.
In view of the foregoing, a detection-type lighting device, which is capable of actually reflecting the condition that a heat source is entering the monitored zone without the additional temperature transducer, is an object to be solved in this technical field.